This disclosure generally relates to non-destructive inspection of structures or parts, and more particularly to systems and methods for characterizing or evaluating anomalies, such as wrinkles, in a laminate structure, such as a composite structure or similar structure.
New, lightweight composite materials and designs are being used more extensively in the aerospace industry for commercial aircraft and other aerospace vehicles, as well as in other industries. The structures using these composite materials may be formed using multiple plies or layers of fiber-reinforced plastic material that may be laminated together to form a lightweight, high-strength structure. Fabrication of composite laminate structure for aerospace applications can result in unwanted out-of-plane wrinkling of plies that can impact performance of the structure based on the size of the wrinkle. Quality assurance and certification for production parts in industries such as the aircraft industry requires that the part be built to meet certain design standards and specifications. For some parts there may be a standard acceptance criteria based on wrinkle size. Accordingly being able to accurately detect and measure the size of any wrinkles in a structure or part is desirable.
Some wrinkles can be identified visually from the surface. However, they cannot be quantified visually, so in an abundance of caution the worst case may be assumed unless means for measuring the size of the wrinkle (often in terms of length L divided by height D) can be provided. Also, wrinkles deeper in the structure cannot be seen visually from the surface at all. Ultrasonic methods have been developed to identify and quantify wrinkles. However, the main drawback of ultrasonic methods is that they cannot “see” beneath a wrinkle (and no access is available to the back side of the structure), so the amount of “good” material is unknown. Therefore, the maximum thickness of a wrinkle from its highest peak to the back surface may have to be assumed. This may result in overly conservative knockdowns of strength predictions, and needless and costly repairs. Another drawback of the ultrasonic method in general is that it takes significant time to collect the data. If a means were available to speed up the process through another inspection method—and still identify and/or quantify the size of wrinkles—that would be advantageous. In particular, processes for fabricating fuselages and fuselage sections could benefit from a wide-area method to detect and quantify wrinkles.